Plant Guide for Purple Threeawn (Aristida Purpurea)

Natural Resources Conservation Service Plant Guide

PURPLE THREEAWN Uses Forage value of purple threeawn depends largely on the Aristida purpurea Nutt. other species growing in association in the Plant Symbol = ARPU9 region. In the Southwest, where forage is limited, purple threeawn is considered good spring forage while the plants remain green. In Arizona and New Mexico its abundance and fair palatability make purple threeawn a highly important source of forage. In northern areas where more palatable forage grasses are available, threeawn is considered weedy with little value (Stubendieck et al. 1994; USDA, 1937). Purple threeawn is popular among horticulturalists for use in low water landscaping, especially in the Southwestern United States. Its reddish purple coloring and compact bunchgrass habit make it desirable. It spreads by seed readily however and can overwhelm landscape elements and become a nuisance. Seed also sticks to animal fur and human socks. Seed heads should be removed before maturity to prevent spread (Xeriscape Today 2010).

Purple threeawn provides some cover to small mammals and reptiles in sparsely vegetated desert areas. Native bees will make nests in the root structure.

Status Please consult the PLANTS Web site and your State Department of Natural Resources for this plant’s current status (e.g., threatened or endangered species, state noxious status, and wetland indicator values).

Description This species has been separated in the past into several distinct species. However, the characteristics used to Purple threeawn. Robert Soreng @ USDA-NRCS PLANTS Database. separate these taxa such as culm height, beak length and awn length are highly variable within populations Alternate Names and even on the same plant (Cronquist et al. 1977). The Common Names: wiregrass, red threeawn, dogtown PLANTS Database currently recognizes a single grass, prairie threeawn species with five varieties: purple threeawn (A. purpurea var. purpurea), Fendler’s threeawn (A. p. Scientific Names: A. longiseta var. fendleriana), blue threeawn (A. p. var. nealleyi), Parish’s threeawn (A. p. var. parishii), and Wright’s threeawn (A. p. var. wrightii).

Purple threeawn is a short-lived native perennial warm season bunchgrass with densely tufted culms averaging 6 to 30 inches tall. The leaves are mostly basal with blades 1 to 10 inches long. The leaves are very narrow; less than 2 mm wide, and involute or rolled. The ligule is a membranous based ring of hairs 0.5 mm long. The inflorescence is a narrow panicle, 2 to 8 inches long with the lower branches ascending or spreading. The spikelets are reddish to purple colored. The floret bears a twisted awn column which divides into three awns Pests and Potential Problems 3/4 to 4 inches in length (Welsh et al. 2003). There are no pests or potential problems documented for this species. Members of the genus have Kranz anatomy and C4 photosynthesis. (Voznesenskaya,et al. 2005). Environmental Concerns Purple threeawn is native to arid locations in western Distribution: Purple threeawn occurs in western North North America and poses no concern to native America from the west coast eastward to Minnesota, plant communities. However it spreads Illinois and Louisiana. There are also disjunct quickly into disturbed areas and can be documented occurrences in Vermont, North Carolina considered invasive in certain situations. Its and South Carolina. For current distribution, please dominance may be indicative of poor grazing consult the Plant Profile page for this species on the management, especially in the Northern Great PLANTS Web site. Plains. Habitat: Purple threeawn inhabits dry coarse or sandy Once matured, the long awns on the seed head can soils in desert valleys and foothills. It grows in a become problematic. The awns and sharp seed variety of plant communities including: creosote bush, can become lodged in the soft tissues of the blackbrush, shadscale, greasewood, pinyon-juniper and mouth and nose developing into abscesses ponderosa pine (Welsh et al. 2003). It is often found which are extremely painful. Animals will growing in association with sand dropseed, typically avoid eating threeawn when other needleandthread, and bluebunch wheatgrass (Monsen more palatable forage is available. The awns et al. 2004). may also decrease value of sheep wool. Purple threeawn quickly invades roadsides, animal burrows and other areas where the soil is disturbed.

Adaptation Purple threeawn is very drought tolerant and is generally adapted to sites receiving 6 inches or more annual precipitation. Plants are hardy to -10° F and suggested for use in USDA zone 6 (Mountain States Wholesale Nursery 2001).

Establishment Warm to hot temperatures improve germination of purple threeawn. Evans and Tisdale (1972) recorded little germination before seeds were subjected to air temperatures of 104° F. Other studies show optimum germination between 50 and 86° F (Eddleman 1978).

Purple threeawn can be seeded alone or in mixtures Purple threeawn florets. Bruce Leander, Ladybird Johnson with other native species (Monsen et al. 2004). Drill Wildflower Center. seeding to a depth of 1/2 to 1 inch is recommended. The full stand seeding rate of 4 lbs/ac Pure Live Seed Seeds and Plant Production (PLS) provides an average of 25 seeds/sq ft (Ogle et The USDA-NRCS Tucson Plant Materials Center al., 2014). (2004) recommends planting purple threeawn with 24 to 38 inch row spacing for seed De-awned seed can be drill seeded; however USDA- production to allow for between row NRCS (2004) suggest that de-awning may reduce seed cultivation. Narrower row spacing can be used quality. but seed yields and stand longevity may be reduced. Management

Grazing should be deferred for two or more seasons to allow plants to establish (Ogle et al. 2011).

Purple threeawn increases under grazing because other more palatable bunchgrasses are favored by livestock. Plant Industry. Lincoln, Nebraska.USDA, Forest Seed is drilled in late summer to early fall into a firm, Service. 1937. Range Plant Handbook. 532 p. weed free seed bed. Fields are irrigated to USDA, Natural Resources Conservation Service. 2004. prevent crusting and to aid stand Native Seed Production. USDA-NRCS in establishment. After establishment fields are cooperation with Coronado Resource irrigated to field capacity in late fall. Conservation and Development Area, Inc. Established fields are irrigated if necessary in Voznesenskaya, E.V., Koteyeva, N.K.; Chuong, spring through the boot stage. Overhead S.D.X.; Edwards, G.E.; and Franceschi, V.R. irrigation should be avoided during flowering. 2005. Functional compartmentation of C4 photosynthesis in the triple-layered chlorenchyma Seed is harvested in Tucson from May to July when of Aristida. Functional plant biology. 32 (1): 67- seed is in the hard dough to mature stage. Some 77. lodging may occur. Seed can be stripped for maximum Welsh, S.L., Atwood, N.D., Goodrich, S., and L.C. yields. Direct combining or swathing and windrowing Higgins. 2003. A Utah Flora. Third Edition, provide satisfactory results. revised. Brigham Young University, Provo, UT. Xeriscape Today. www.xeriscape-today.com Visited Awns are removed with a hammermill at moderate January 21, 2014. speed, and the seed is cleaned with air-screening. Weed seed can be removed using an indent or disc cleaner.

Cultivars, Improved, and Selected Materials (and area of origin) Common seed of purple threeawn is available commercially.

References Cronquist, A., Holmgren, A.H., Holmgren, N.H., Reveal, J.L. and P.K. Holmgren. 1977. Intermountain Flora. Volume 6: the Monocotyledons. Columbia University Press. New York, NY. 584p. Eddleman, L.E. 1978. Survey of viability of indigenous grasses, forbs and shrubs. Annual Progress Report. RLO-2232-T2-3. Prepared for US Energy Research and Development Administration. Evans, G.R and E.W. Tisdale. 1972. Ecological characteristics of Aristida longiseta and Agropyron spicatum in west-central Idaho. Ecology. 53: 137-142. Monsen, S.B., Stevens, R. and N. Shaw. 2004. Grasses. In: S.B. Monsen, R. Stevens, and N.L. Shaw [compilers]. Restoring western ranges and wildlands. Fort Collins, CO: USDA Forest Service, Rocky Mountain Research Station. General Technical Report RMRS-GTR-136-vol-2. p. 295-424. Mountain States Wholesale Nursery. http://www.mswn.com/ Visited January 20, 2014. Ogle, D., St. John, l. Stannard, M., Cornwell, J, Holzworth, L. 2011. Technical Note 10: Pasture and Range Seedings – Planning, Installation, Evaluation, Management. USDA-NRCS Boise, ID-Salt Lake City, UT-Spokane, WA. 35p. Ogle, D., St. John, l. Stannard, M., Holzworth, L., Tilley, D. 2014. Technical Note 24: Conservation Plant Species for the Intermountain West. USDA- NRCS Boise, ID-Salt Lake City, UT-Spokane, WA. 73 p. Stubbendieck, J., G.Y. Friisoe, & M.R. Bolick. 1994. Weeds of Nebraska and the Great Plains. Nebraska Department of Agriculture, Bureau of Citation D. Tilley and L. St. John, L. 2013. Plant guide for purple needlegrass (Aristida purpurea). USDA-Natural Resources Conservation Service, Plant Materials Center, Aberdeen, Idaho 83210.

Published February 2014

Edited: 21Jan2014ls; 27Jan2014jab

For more information about this and other plants, please contact your local NRCS field office or Conservation District at http://www.nrcs.usda.gov/ and visit the PLANTS Web site at http://plants.usda.gov/ or the Plant Materials Program Web site http://plant- materials.nrcs.usda.gov. PLANTS is not responsible for the content or availability of other Web sites

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